Centralizers for centralizing well casings

ABSTRACT

A centralizer for centralizing a pipe downhole in a well is provided. The centralizer includes a plurality of arcuate cuffs having first and second ends. The cuffs are affixed adjacent to the pipe&#39;s exterior wall, and positioned circumferentially adjacent around the pipe. The cuffs are flexible so as to be positioned in a first condition wherein the cuffs are retracted radially inward so as to be substantially flat against the pipe&#39;s exterior wall. The centralizer includes a lock for maintaining the cuffs substantially flat against the pipe&#39;s exterior wall until the centralizer has been transported downhole. Further, the centralizer includes an actuator for unlocking the lock so as to allow the cuffs to expand radially outward to form a loop wherein the loop has a central axis parallel to pipe&#39;s longitudinal axis. Preferably, the centralizer includes a collar causing the cuffs to all expand or retract together.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 14/338,620 filed on Jul. 23, 2014 which claims thebenefit of U.S. Provisional Patent Application Ser. No. 61/858,063 filedon Jul. 24, 2013 and, both of which are hereby incorporated herein byreference in their entirety.

BACKGROUND

This disclosure relates generally to the construction of subterraneanwells. More particularly, this disclosure relates to methods andapparatus for centering a casing within a well, particularly an oil orgas well. Still more particularly, this disclosure relates to methodsand apparatus for centering a casing within an oil and gas well suchthat cement can be evenly distributed within the annulus disposedbetween the casing to enable zonal isolation (i.e. no fluid or gasmigration).

A well is a subterranean boring from the Earth's surface that isdesigned to find and acquire liquids or gases. Wells for acquiring oilare termed “oil wells”. A well that is designed to produce mainly gas iscalled a “gas well”. Typically, wells are created by drilling a bore,typically 5 inches to 40 inches (12 cm to 1 meter) in diameter, into theearth with a drilling rig that rotates a drill string with an attachedbit. After the hole is drilled, sections of steel pipe, commonlyreferred to as “casings” and which are slightly smaller in diameter thanthe borehole, are dropped “downhole” into the bore for obtaining thesought after liquid or gas.

The difference between the diameter of the wellbore and the outerdiameter of the casing results in an annular space therebetween. Whencompleting oil and gas wells, it is desirable to seal the annular spacewith cement. The cement is pumped into the annular space, replacing thedrilling mud therein. Once the annular space is filled with cement, thecement is allowed to harden to seal the well. To properly seal the well,the casing is preferably positioned so that it is in the middle orcenter of the wellbore such that the annular space has a constant orsubstantially constant radial width moving circumferentially about thecasing. The casing and cement provide structural integrity to the newlydrilled wellbore and provide isolation of high pressure zones. Thus,centralizing a casing inside the annular space is facilitates a reliableseal, and thus good zonal isolation. With the advent of deeper wells andhorizontal drilling, centralizing the casing has become more important,yet more difficult to accomplish.

A traditional method to centralize a casing is to attach centralizers tothe casing prior to its insertion into the annular space. Mosttraditional centralizers have tabs, wings or bows that exert forceagainst the inside of the wellbore to keep the casing somewhatcentralized. The centralizers are commonly secured at intervals along acasing string to radially offset the casing string from the sidewall ofa borehole in which the casing string is positioned. Centralizers centerthe casing string within the borehole to provide a generally continuousannulus between the casing string and the sidewall of the borehole. Thispositioning of the casing string within a borehole promotes uniform andcontinuous distribution of cement slurry around the casing string.Uniform cement slurry distribution results in a cement liner thatreinforces the casing string, isolates the casing from corrosiveformation fluids, prevents unwanted fluid flow between penetratedgeologic formations, and provides axial strength. In general, 100%standoff is achieved once the casing is radially centralized within theborehole or the annulus with the previous casing.

A bow-spring centralizer is the most common type of centralizer. Itemploys flexible bow-springs to provide offset between the casing andwellbore sidewall. Bow-spring centralizers typically include a pair ofaxially-spaced and generally aligned circular collars that are coupledby multiple bow-springs. The bow-springs expand outwardly from thecollars to engage the borehole sidewall to center a pipe receivedaxially through the collars. Configured in this manner, the bow-springsprovide stand-off from the borehole, and flex inwardly as they encounterborehole obstructions, such as tight spots or protrusions into theborehole, as the casing string is installed into the borehole.Elasticity allows the bow-springs to spring back to substantially theiroriginal shape after passing an obstruction to maintain the desiredstand-off between the casing string and the borehole. Examples of suchbow springs are disclosed in U.S. Pat. No. 4,545,436 and Great BritainPatent No. 2242457 which both disclose casing centralizers having aplurality of bows springs which are connected to first and secondcollars. The collars surround the well casing, and one or both of thecollars slide longitudinally upon the pipe when the bow spring isdeformed upon engaging the well bore sidewall.

The use of bow-spring centralizers presents a number of disadvantagesand their installation can be problematic. To achieve the desiredcentralization, bow centralizers are designed so that, prior toinstallation. the bow-springs extend beyond the inside diameter (“ID”)of the wellbore. The larger diameter of said bow-springs requires themto be retracted from the force of pushing it down inside the casing orwellbore. This causes kinetic friction when slid down the hole(requiring running force) and also static friction when engagingrestrictions or obstructions (requiring starting force). This frictioncan sometimes prevent the casing from getting to the desired depth.Further, the radial configuration of the bow-springs causes the springforce of one bow-spring to be counteracted by the bow-springs on theopposite side of the casing. This results in a restoring force thatdiminishes as the casing approaches center, thereby making bettercentralization require greater and greater spring forces. Furthermore,increased spring forces also increases running and starting resistance.Therefore, a balance is sought between the needed forces to sufficientlycentralize the casing and the increased resistance that these springforces create. A further disadvantage of the bow spring centralizers canarise in wells where the open hole is under-reamed (i.e. the hole islarger than the previous casing shoe). In such cases, centralization isparticularly difficult as the bows have to collapse through therestriction and expand sufficiently to centralize the casing in largeropen hole.

Yet another disadvantage of bow spring centralizers is that the bowsprings obstruct the pumping of cement downhole. After being positioneddownhole, the bow springs project radially outward from the casing likespokes to engage the well bore's cylindrical wall. These bow springs canblock the proper downward flow of the cement slurry or can create voidsin the annular cement structure.

Various attempts have been made to develop centralizers that overcomesome of these problems. U.S. Pat. No. 6,871,706 discloses a centralizerthat requires the bending of a retaining portion of the collar materialinto a plurality of aligned openings, each to receive one end of eachbow-spring. This requires that the coupling operation be performed in amanufacturing facility using a press. The collars of the centralizer arecut with a large recess adjacent to each set of aligned openings toaccommodate passage of a bow-spring that is secured to the interior wallof the collar. Unfortunately, the recess substantially decreases themechanical integrity of the collar due to the removal of a large portionof the collar wall to accommodate the bow-springs.

U.S. Patent Publication 20120279725 and U.S. Pat. No. 7,857,063 describecentralizers that have a minimal radial expansion prior and during thecasing's transportation downhole. Only after the casing is in place arethe centralizer tabs expanded radially outward. This reduces the amountof friction that the casing string encounters as it is dropped downhole.Furthermore, the tabs extend laterally relative to the pipe's centralaxis in a manner that minimizes the obstruction to the flow of cement asit poured downhole. Unfortunately, these centralizers are not suitablefor traditional metal well casings that provide minimal radialexpansion. Instead, the centralizers are useful only for centralizingtubular members capable of substantial expansion so as to force thecentralizer tabs to engage the borehole wall.

Thus, there is a significant need for an improved casing centralizerthat provides reduced friction as the centralizer is transporteddownhole.

There is also a need for an improved casing centralizer that providesincreased centralizing force for maintaining a casing in the center of awell bore.

Still there is an additional need for an improved casing centralizerthat provides minimal impedance to the flow of cement as cement ispumped downhole in the annular space between the casing string and thewell bore wall.

Advantageously, the improved centralizer would provide reducedmanufacturing and installation costs, and provide an improved ease ofrunning the casing string downhole into the well bore.

BRIEF SUMMARY OF THE DISCLOSURE

Embodiments disclosed herein address the aforementioned disadvantages byproviding an improved centralizer for centralizing a pipe downhole in awell. In general, embodiments of centralizers described herein can beintegrated into the pipe so as to include the pipe's cylindricalexterior sidewall and central conduit which defines the pipe'slongitudinal axis. Alternatively, the centralizer can include astructure, such as a circular band, for affixing to a pipe, such as foraffixing to a pipe immediately prior to the pipe being transporteddownhole into a well.

At least one embodiment of a centralizer described herein includes aplurality of cuffs. The cuffs are preferably made from metal, whichpreferably is a traditional spring steel to provide flexibility but alsoto store substantial mechanical spring energy. The lengths andthicknesses of the cuffs can be determined by those skilled in the artdepending on the amount of space desired between the casing andwellbore, the weight and diameter of the casing, and the amount of forceneeded to be exerted by the cuffs.

The cuffs radially extend in an arcuate manner from the pipe. Morespecifically, each cuff includes first and second ends affixed adjacentto a pipe's cylindrical exterior wall in a manner that forms a loophaving an opening defining a central axis. Each cuff is affixed so as toalign the loop's central axis to be parallel to the pipe's centralconduit. By providing the loop having an axis parallel to the pipe'scentral conduit, the centralizer minimizes any obstruction to the flowof cement downhole. The centralizer may include any number of cuffs.However, it is preferred the centralizer includes at least two cuffs andthat the cuffs are evenly spaced around the pipe and circumferentiallypositioned next to each other forming a flower-like pattern. Thus, acentralizer having two cuffs preferably has the cuffs positioned180.degree. from one another. A centralizer having three cuffs has thecuffs positioned 120.degree. around the pipe, etc. etc.

Of importance, the arcuate cuffs are capable of being retracted prior tothe centralizer being positioned downhole, and expanded radially outwardafter the centralizer has been positioned downhole in a well. Each cuffsfirst end is affixed to the pipe's exterior wall. The cuffs first endmay be affixed to the pipe's exterior wall by any fastener constructionknown to those skilled in the art including welding, threaded fasteners,rivets, or flanges. Meanwhile, each cuffs second end is selectivelyaffixed adjacent to the pipe's exterior wall in a manner that the cuffssecond end is allowed to move circumferentially upon the pipe's exteriorwall from a first position wherein the cuff is flexed to form apartially circular shape which is substantially flat against the pipe'sexterior wall to a second position wherein the center of each of thecuffs extend radially outward so that the cuff forms a loop shape.

Moreover, the centralizer includes a lock for locking the cuffs in aradially retracted condition wherein the cuffs are flexed to besubstantially flat against the pipe's exterior wall. When a lock isselectively unlocked, a cuffs second end is free to movecircumferentially around the pipe. Importantly, the cuffs areconstructed in the manner of leaf springs to store mechanical springenergy when compressed flat against a pipe's exterior wall. When thelock is released and the cuffs second ends are free to movecircumferentially around the pipe, the mechanical spring energy isreleased allowing the cuffs to spring back into a condition wherein eachcuff expands radially outward to form a loop.

The lock may be constructed in various manners known to those skilled inthe art for selectively locking the cuffs' second ends adjacent to thepipe's exterior wall at a distance from the cuffs' first end. Moreover,the centralizer includes an actuator for selectively unlocking the lockonly after a pipe has been positioned downhole in a well. Numerousactuators for selectively unlocking the lock can also be devised bythose skilled in the art. Examples of suitable locks include simple pinswhich can be retracted using servo-motors or the like. Another exampleis to actuate locking pins using a release system that is actuated byconverting the pressure-expansion of the casing into a mechanicalunlocking device. Alternatively, bolts can be utilized which can bedisengaged using motors or pyrotechnic bolt cutters. Alternatively, thecuffs may be locked in place utilizing a cylindrical hollow housinghaving a shape similar to a pipe with open ends for covering andmaintaining the cuffs in a retracted condition. To release the cuffs,the housing is simply moved longitudinally in a telescopic mannerrelative to the pipe to allow the cuffs to expand. This can beaccomplished using motors or springs, or other constructions as can bedetermined by those skilled in the art.

Moreover, though not preferred, separate locks may be provided to eachcuff so that each cuff can be controlled to expand individually withoutaffecting other cuffs. However, as explained in greater detail below, itis preferred that the centralizer cuffs are connected so as to beradially compressed together and radially expanded together.

In at least one embodiment, the centralizer includes a collar whichcircumferentially surrounds the pipe and is capable of rotation aboutthe pipe. The collar affixes to each of the plurality of cuffs secondends so that each of the cuffs second ends rotate together about thepipe. Thus, when one cuff has been retracted radially inward to acompressed condition so as to be substantially flat against the pipe'sexterior wall, all other cuffs of the centralizer are also compressedradially inward to a compressed condition. Conversely, when the collarhas rotated so that a first cuff has expanded to a second conditionwherein the first cuff forms a loop, all other cuffs must also expandradially outward to form loops. Again, various collar constructions maybe designed by those skilled in the art. In a preferred embodiment, thecollar is a hollow cylinder including a plurality of sidewall openingsfor allowing the plurality of cuffs to expand radially. The collar mayaffix to the cuffs second ends utilizing various fasteners known tothose skilled in the art including threaded fasteners, welding orrivets. In a preferred embodiment, the collar affixes to the cuffs'second ends by a simple flange construction.

To retract the cuffs into a compressed radially inward condition, thecollar is rotated relative to the pipe so that each cuffs second end ispulled away from the cuffs respective first end. Substantial rotationalforce may have to be exerted upon the collar depending upon the amountof mechanical spring force exerted by each of the cuffs during rotation.Once the collar has been rotated to the point that the cuffs are flatagainst the pipe's exterior wall, the collar is locked in place by alock, thereby storing substantial mechanical spring energy in the cuffswhich are attempting to expand back to their prior arcuate loop shape.

The collar may be locked in place utilizing various locks that can bedeveloped by those skilled in the art. For example, the collar can besimply affixed in place utilizing one or more bolts which can be removedby motors or pyrotechnic bolt cutters. Alternatively, the collar can beaffixed to the pipe utilizing a meltable solder. Once the centralizerhas been positioned downhole, heat can be introduced to the centralizersuch as by the introduction of hot fluid, such as a hot mud slurry, intothe pipe bore, or by utilizing an induction heater positioned interiorto the pipe adjacent to the centralizer. Heat is introduced until thesolder has reached the temperature upon which it starts to melt and theload exerted by the cuffs is sufficient to overcome the solder'sadherence, and the collar rotates and the cuffs radially expand.

In an alternative embodiment, the collar includes a notch, and a pin ispositioned within the notch so as to prevent rotation of the collaruntil the pin has been retracted. Again, retraction of the pin can beaffected by various constructions as can be determined by those skilledin the art such as by using servo-motors. Alternatively, the pin may besoldered in place. The pin is biased to retract such as by utilizing aspring or force exerted by the collar so that melting of the soldercauses the pin to retract and the collar to rotate. Again, melting ofthe solder can be accomplished utilizing heated fluid or an inductionheater within the pipe's central conduit.

As would be appreciated by those skilled in the art, embodiments ofcentralizers described herein may require an actuator for selectivelyunlocking the lock, which as described above may include a retractablepin or solder. For example, the actuator may simply be the introductionof heat such as by heated fluid or an induction heater as describedabove. In alternative embodiments, the actuator may comprise a timerconnected to the lock for selectively unlocking the lock. For example,the centralizer may include a timer, heater and power source adjacent toa solder lock. Once the centralizer has been positioned downhole, thetimer can trigger the power source to provide heat to the solder causingthe solder to melt, collar to rotate, and cuffs to expand.Alternatively, the timer and power source may be connected to anelectric motor, bolt cutter or other apparatus for unlocking the lockand allowing the collar to rotate.

In still an additional embodiment, the centralizer's actuator includes areceiver for receiving a signal downhole. The receiver may beconstructed to receive radio frequency (“RF”) signals or acousticsignals which are transmitted by a transmitter located above ground.Alternatively, the signal may be an electrical signal transmitted fromabove ground through electrically conductive metal casing to thecentralizer downhole. Upon receipt of the desired signal, which may becoded to prevent inadvertent deployment, the receiver causes the lock tounlock. For example, where the collar is locked by meltable solder, thereceiver may be connected to a heater and power supply. Upon detectionof a signal downhole, the receiver activates the heater so as to meltthe solder and cause the collar to rotate. Again, the receiver may beconnected to other constructions such as servo-motors, bolt cutters orthe like for causing the lock to unlock to permit rotation of thecollar. Furthermore, the actuator may include a computer processorconnected to the signal receiver for determining when the lock should beunlocked. For example, the processor may analyze the signal to determineif it is valid or to determine whether other conditions have been met topermit deployment, such as whether the centralizer has been properlypositioned downhole.

In still an additional embodiment, the actuator includes a strain gaugeaffixed to the centralizer or affixed directly to the pipe fordetermining whether the pipe has deformed such as by an increase inpressure within the pipe. The actuator further includes a processor andpower source connected to the strain gauge. The processor analyzesdeformation of the pipe, as measured by the strain gauge, such that apredetermined deformation triggers the actuator to unlock the lockrestraining the cuffs. For example, once the pipe has been transporteddownhole, it is common for well builders to pressurize the pipe, such asto 5,000 PSI, to ensure pipe integrity. The pressurizing of the pipecauses deformation of the pipe which can be measured by traditionalstrain gauges. The processor can actuate release of the cuffs upon thepipe being pressurized above a certain pressure threshold.Alternatively, the processor may unlock the lock so as to release thecuffs only after receipt of a series of pressure pulses introduced intothe pipe bore so as to provide additional protection against inadvertentdeployment. The strain gauge and processor may be connected to variousmeans for unlocking the lock as described above, such as including aheater for melting solder, or motors, or bolt cutters for disengaging abolt.

Still an additional embodiment of the actuator described herein utilizesthe introduction of high pressure into the pipe after the pipe has beentransported downhole so as to allow radial expansion of the cuffs. Forthis embodiment, the collar includes a notch. Once the collar has beenrotated so as to retract the cuffs, the centralizer lock includes aretractable pin which is positioned within the notch so as to preventthe collar from rotating until the pin has been retracted. The pin isbiased to retract such as by a spring or by the collar having a shoulderattempting to push the pin into a refracted condition. However, the pinis constrained from retracting by a ring which circumferentiallysurrounds the pipe adjacent to the collar in a manner so as to engagethe pin. The ring includes a recess and the ring is rotatable from afirst position wherein the recess does not receive the pin to a secondposition wherein the ring recess does receive the pin. The rotation andalignment of the recess to accept or not accept the pin can beaccomplished by utilizing various constructions known to those skilledin the art including the use of servo-motors, springs coupled with boltcutters, etc. For example, the actuator may include a strain gauge orsignal receiver for receiving a pressure pulse, RF or acoustic signalcoupled to a power servo-motor so as to cause the ring to rotate toalign the recess with the retractable pin thereby causing the pin toretract and cuffs to expand. However in the preferred embodiment thatutilizes pressure actuation, the actuator includes a strap which atleast partially circumferentially surrounds the pipe. Preferably, thestrap is wrapped between one and two times around the pipe. The straphas a first end affixed to the pipe and a second end affixed to thering. As would be understood by those skilled in the art, expansion ofthe pipe would cause the strap to tighten around the pipe to place thestrap in tension and thereby pull and rotate the ring in a firstdirection. Meanwhile, the ring is positioned such that upon the strappulling the ring in the first direction by a predetermined distance willcause the ring recess to align with the pin so as to allow the pin toretract from the collar's notch.

Preferably, the actuator includes a plurality of ratcheting teethpositioned to project into indents formed into the ring. The teeth areangled and biased so as to allow the ring so as to rotate only in thefirst direction so that upon an increase in pressure within the pipe,the pipe rotates in the first direction, but a subsequent decrease inpressure within the pipe does not cause the ring to rotate in theopposite direction. Moreover, the actuator includes a spring to maintainthe strap in tension even if the pipe interior pressure is decreased.This construction allows one to pressure pulse the interior of the pipe(including an increase in pressure and decrease in pressure) toincrementally rotate the ring about the pipe until rotationally aligningthe pin with the ring's recess so as to allow the pin to retract fromthe collar's notch so as to allow the cuffs to expand. Advantageously,this embodiment does not require a downhole power supply.

Embodiments of centralizers described herein preferably have minimal anda relatively smooth cross-section prior to being transported downhole soas to substantially reduce any friction that the pipe encounters as itis transported downhole as compared to prior art centralizers. The crosssection also preferably incorporates a profile to prevent the rotatingcollar from coming into contact with the formation in order to minimizethe frictional forces acting against the rotation of the ring

Advantageously, combining the force of the cuffs together provides asubstantial increase in centralizing force as compared to prior artcentralizers.

An additional advantage is that the improved centralizer aligns the cuffloops with the flow of cement so as to minimize the impedance of cementflow as it is pumped downhole.

Still an additional advantage is that the centralizer can bemanufactured and installed relatively inexpensively with little trainingrequired for well personnel.

Other features and advantages of embodiments described herein will beappreciated by those skilled in the art upon reading the detaileddescription which follows with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a first embodiment of a cuffcentralizer in accordance with the principles described herein;

FIGS. 2A-2C are perspective views of the cuff centralizer shown in FIG.1 illustrating the operation of the actuator system;

FIG. 3A is a perspective view of the actuator system for use with thecuff centralizer illustrated in FIGS. 1 and 2A-2C;

FIG. 3B is an exploded perspective view of the actuator illustrated inFIG. 3A;

FIG. 4A is a perspective view of a second embodiment of a cuffcentralizer in accordance with the principles described herein whereinthe cuffs are retracted;

FIG. 4B is a cutaway view of the lock and actuator illustrated in FIG.4A;

FIG. 5A is a perspective view of the cuff centralizer illustrated inFIG. 4A wherein the centralizer has deployed;

FIG. 5B is a cutaway view of the lock and actuator illustrated in FIG.5A;

FIG. 6A is cutaway view of a lock embodiment including a soldered pin;

FIG. 6B is a cutaway view of the pin illustrated in FIG. 6A wherein thesolder has been melted and the pin has retracted;

FIG. 7A is a perspective view of a first embodiment of a cuff inaccordance with the principles described herein for use with acentralizer in a retracted condition;

FIG. 7B is a perspective view of the cuff shown in FIG. 7A illustratedin an expanded condition;

FIG. 8 is a second embodiment of a cuff in accordance with theprinciples described herein for use with a centralizer includingmultiple layers of material;

FIG. 9A includes perspective views illustrating the cuff centralizers inretracted and expanded conditions;

FIG. 9B is a side cutaway view of a cuff centralizer in accordance withthe principles described herein illustrating how the cuffs affix to awell pipe and rotating collar; and

FIG. 9C are bottom cutaway plan views illustrating the cuff centralizerin a wellbore in retracted and expanded conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following discussion is directed to various exemplary embodiments.However, one skilled in the art will understand that the examplesdisclosed herein have broad application, and that the discussion of anyembodiment is meant only to be exemplary of that embodiment, and notintended to suggest that the scope of the disclosure, including theclaims, is limited to that embodiment.

Certain terms are used throughout the following description and claimsto refer to particular features or components. As one skilled in the artwill appreciate, different persons may refer to the same feature orcomponent by different names. This document does not intend todistinguish between components or features that differ in name but notfunction. The drawing figures are not necessarily to scale. Certainfeatures and components herein may be shown exaggerated in scale or insomewhat schematic form and some details of conventional elements maynot be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . . ” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection, or through anindirect connection via other devices, components, and connections. Inaddition, as used herein, the terms “axial” and “axially” generally meanalong or parallel to a central axis (e.g., central axis of a body or aport), while the terms “radial” and “radially” generally meanperpendicular to the central axis. For instance, an axial distancerefers to a distance measured along or parallel to the central axis, anda radial distance means a distance measured perpendicular to the centralaxis. Any reference to up or down in the description and the claims willbe made for purposes of clarity, with “up”, “upper”, “upwardly” or“upstream” meaning toward the surface of the borehole and with “down”,“lower”, “downwardly” or “downstream” meaning toward the terminal end ofthe borehole, regardless of the borehole orientation. As used herein,the term “pipe” is intended to be interpreted in the traditional senseas a cylindrical structure having an exterior wall and a centralconduit. Furthermore, the term “pipe” is intended to include traditionalwell casings, casing strings, and casing couplers which connect casingsto form a casing string.

With reference to the figures and particularly FIG. 9C, an embodiment ofa centralizer 1 in accordance with the principles described herein isshown. Centralizer 1 is intended for centralizing a pipe 3 having acylindrical exterior wall 5 and central conduit 7 within a wellbore 13.The centralizer 1 may be permanently affixed and integrated into theexterior of the pipe, such as for use as a pipe coupling for connectingvarious lengths of pipe, commonly referred to as casings, together.Alternatively, as best illustrated in FIGS. 3A and 3B, the centralizer 1may include one or more clamp bands 21 for affixing the variouscentralizer components to a pipe 3 either prior to shipment to a well orimmediately prior to a pipe being transported downhole into a well. Asillustrated in FIGS. 3A and 3B, the clamp bands 21 form a generallycircular shape and can be affixed to a pipe utilizing well knownfastener constructions such as threaded fasteners for preventing theband for rotating about the pipe.

The centralizer 1 includes a plurality of cuffs 29. As illustrated inFIGS. 7A, 7B and 8, the cuffs are elongate, arcuate and have first andsecond ends, 31 and 33 respectively. The cuffs operate in a similarmanner to leaf springs, and thus are preferably made of a traditionalmetal for storing mechanical spring energy, such as spring steel. Thecuffs may incorporate various alloys or have a protective coating toprotect them against environmental conditions.

As illustrated in FIGS. 9A-9C, each cuffs first end 31 and second end 33is affixed adjacent to the pipe's cylindrical exterior wall 7. The cuffs29 can be compressed radially inward into a first condition so as to besubstantially flat against the pipe's exterior wall and locked in place.Alternatively, each of the cuffs 29 can be expanded radially outward toform a loop 35 wherein each cuffs first end 31 and second end 33 havebeen allowed to constrict together. Since the cuffs are constructed asleaf springs attempting to form a loop construction, each of the cuffsstore mechanical spring energy when positioned so as to be in theradially retracted condition flat against the pipe exterior sidewall. Asillustrated in FIGS. 4 and 5, the cuffs 29 are arranged about the pipe 3so that the cuffs' loops 35 define a central axis 37 which is parallelto the pipe's longitudinal axis 9.

Preferably the centralizer cuffs 29 are connected together so as to beradially compressed together and radially expanded together. To thisend, preferably the centralizer 1 includes a collar 51. For thisembodiment, each of the cuffs' first ends 31 are affixed to the pipe soas to be prevented from rotating relative to the pipe. Meanwhile, thecollar 51 has a hollow cylindrical structure having an inner diameterlarger than the outer diameter of the pipe 3 so as to circumferentiallysurround the pipe and be capable of rotation about the pipe. The collar51 affixes to each of the cuffs' second ends 33 so that rotation of thecollar 51 causes each of the cuffs' second ends 33 to rotate about thepipe adjacent to the pipe's exterior sidewall 5. The collar 51 includessidewall openings 53 allowing each of the cuffs 29 to expand radiallyoutward through the collar 51.

As best illustrated in FIG. 9A, the centralizer 1 may include severallongitudinal tiers of cuffs 29 which are capable of contracting andexpanding through multiple longitudinal tiers of openings 53 formed inthe collar 51. In a first rotational position relative to the pipe 3,the collar 51 extends each of the cuffs' first ends 31 away from thecuffs' second ends 33 so as to flatten the cuffs against the pipe'sexterior wall 5. Rotating the collar 51 to a second position, whereinthe cuffs' first and second ends have been contracted together, causesthe cuffs to expand radially outward to form loops 35. The cuffs' firstends 31 can be affixed to the pipe 3 and the cuffs' second ends can beaffixed to the collar 51 utilizing various fasteners known to thoseskilled in the art. As illustrated in FIGS. 7A, 7B, 8 and 9B, in apreferred embodiment the pipe 3 and collar 51 include flanges 55 foraffixing to flanges 39 formed into the first and second ends of thecuffs 29.

The centralizer 1 includes a lock 45 for locking the cuffs in aretracted condition, and an actuator 81 for selectively unlocking thelock only after a pipe has been transported downhole into a well so asto allow the cuffs to expand radially outward. FIGS. 1-4 illustrate afirst preferred embodiment of a lock 45 and actuator 81 for use with thecentralizer 1 described herein. The lock includes a notch 57 formed intothe collar 51. Furthermore, the lock 45 includes a retractable pin 59capable of extending into the notch 37 for preventing rotation of thecollar 51 around the pipe 3. As illustrated in FIGS. 3A and 3B, the pin59 is prevented from rotating about the pipe 3 by a housing and clampband 21. Meanwhile, the actuator 81 includes a ring 83 having a ringrecess 85. The ring has an inner diameter larger than the outer diameterof the pipe 3 so as to receive and rotate about the pipe so that thering recess 85 may be rotated from a first position wherein the recessdoes not align with the pin 59 and the ring prevents retraction of thepin from the collar's notch 57. However, as illustrated in FIGS. 2A-2C,the ring 83 may be rotated in the direction 93 so as to align the ring'srecess 85 with the retractable pin 59. The pin may be biased to retractinto the ring recess 85 utilizing a spring or the like. However, it ispreferred that the pin 59 simply include a tapered end which engages thecollar notch's shoulder 63. Since the collar is biased to rotate in thefirst direction 93 by the spring energy within the cuffs 29, the notch'sshoulder 63 will force the pin to retract into the ring's recess 85 whenproperly aligned.

To rotate the ring, in the embodiment illustrated in FIGS. 1-4, theactuator 81 includes a strap 87 and a ratchet assembly including teeth95 and indents 97. A first end 89 of a strap is affixed to the pipe 3.As illustrated in FIGS. 3A and 3B, the strap's first end may be affixedto the pipe utilizing a tab 89 affixed to clamp band 21 which in turnaffixes to the pipe 3. Meanwhile, the strap's second end 91 affixes to atoothed assembly 99 having a plurality of teeth 95 which are capable ofrotating in an oscillating manner about the pipe 3. Preferably, thetooth assembly 99 is circular so as to circumferentially surround androtate about the pipe. The tooth assembly 99 may include any number ofteeth as can be determined by those skilled in the art. Meanwhile, thering 83 includes a plurality of indents 97 positioned so that as thetooth assembly 99 is rotated in the direction 93, the teeth 95 engageone or more of the ring indents 97 so as to cause the ring to rotate.

The lock 45 and actuator 81 illustrated in FIGS. 1-3 are operated bypressure pulsing pipe 5, such as by cyclically pressurizing the pipe to2500 PSI or above which can be determined depending on the thickness ofthe pipe 3 and other factors. With each pressure pulse, the actuator'sstrap 87 is placed in tension. Because the strap's first end 89 isaffixed to the pipe 3, the strap's second end 91 is made to rotate inthe direction 93. This causes the strap to pull the tooth assembly 99 inthe same direction 93 causing the teeth 95 to engage indents 97 tothereby rotate ring 83 in direction 93. As the pipe is depressurized,the ring 83 maintains its relative rotation relative the pipe 5.However, the strap 87 is pulled back into place by spring 100. As thestrap's second end 91 is pulled, the tooth assembly 99 is rotated in theopposite direction so that teeth 95 are moved to engage new indents 97.This process is repeated, thereby rotationally oscillating the toothassembly 99 until the ring 83 has rotated so as to align the ring recess85 so as to receive pin 59. Once aligned, the pin is retracted intonotch 57 allowing the collar 51 to rotate and the cuffs 29 to expand.

Still additional embodiments of the centralizer lock and actuator areillustrated in FIGS. 4-6. As illustrated, the centralizer 1 includes twolock assemblies 45 requiring two actuators 81. The two locks andactuators are provided for redundancy. However, as would be understoodby those skilled in art, a centralizer 1 as described herein may includeonly one set of these locks and actuators. A first lock simply comprisessolder 71 for maintaining the collar 51 in a first rotational positionwherein the cuffs' first and second ends, 31 and 33, have been pulledapart so as to stretch the cuffs 29 so as to be retracted substantiallyflat against the pipe's exterior wall 5. (See FIG. 4A). The collar maybe soldered directly to the pipe. Alternatively, the actuator mayinclude one or more brake shoes (not shown) which are soldered to thepipe to restrict the collar from rotating. Only after the centralizer 1has been positioned downhole, heat is introduced into the pipe's centralconduit 7 adjacent to the centralizer so as to melt the solder and allowthe collar to rotate. Heat may be introduced in any manner known tothose skilled in the art such as by the pumping of hot water, thepumping of a hot mud slurry, an induction heater or electrically woundcoil heater introduced downhole. Once the solder has melted, themechanical spring energy stored in cuffs 29 causes the collar 51 torotate, and the cuffs to radially expand outward to form loops 35, eachhaving a central axis 37 parallel to the pipe's longitudinal axis 9.(See FIG. 5A).

As also illustrated in FIGS. 4-5, the collar may be locked in the firstrotational position by a retractable pin 59 projecting into a notch 57formed in the collar 51. As illustrated in FIG. 4B, the pin 59preferably has a tapered end 61 which engages the notch's shoulder 63.Due to their tapered shape, the collar attempts to bias the pin toretract. However, the pin is locked in place by solder 71 (See FIG. 6A).Preferably the pin 59 includes a central heating element 65 which uponactivation causes the solder 71 to melt. Once the solder has melted, thepin 59 is able to retract to allow the cuffs 29 to expand. (See FIGS. 5Aand 5B).

As illustrated in FIGS. 4-5, electricity to the heating element 65 ispreferably provided by an electronics package 101 located downhole witha centralizer. The electronics package 101 is illustrated as beingdetached from the pipe 3 and centralizer 1. However, it is preferredthat the electronics package be affixed to the pipe immediately adjacentto the retractable pin so that power can be transmitted as short adistance as possible. The electronics package 101 may include variouscomponents for receiving, analyzing and triggering the heating element65 to melt the solder 71. The components may include one or more generalpurpose computer processors and power sources (such as a battery)capable of withstanding the ambient temperatures and pressures founddownhole in a well. In addition, the electronics package 1 includes areceiver for receiving a signal downhole. The receiver may beconstructed to receive radio signals, acoustic signals or electricalsignals which are transmitted by a transmitter (not shown) located aboveground. Again, various general purpose radio frequency, acoustic orelectrical receivers may be selected or developed without undueexperimentation by those skilled in the art. Where the receiver isconstructed to receive an electrical signal, the electrical signal maybe transmitted through the electrically conductive material forming thepipe 3 which is received by the electronics package 101, and analyzedand processed by a processor, which in turn causes the heater element 65to activate upon receipt of the appropriate electrical signal.Similarly, the electronics package 101 may include a radio frequencyreceiver for receiving radio frequency signals or an acoustic receiverfor receiving lower frequency acoustic signals. Again, the signals canbe processed by the processor connected to a power supply whichactivates the heating element 65 to release expansion of the cuffs 29.In still an alternative embodiment, the electronics package 101 includesa general purpose strain gauge connected to a processor and powersupply. The strain gauge is positioned so as to measure deformation ofthe collar 51 or pipe 3 caused by increased pressure within the pipe'scentral conduit 7. The processor is preprogrammed to trigger activationof the retractable pins' heating element 65 upon the pipe beingpressurized above a predetermined pressure, such as 2,500 lbs. per sq.in., or after the pipe has been pressure pulsed in a predeterminedpattern. Still additional receivers may be selected by those skilled inthe art.

As illustrated in FIG. 9C, the centralizer provides a minimal andrelatively smooth cross-section as it is transported downhole into awell so as to minimize friction and the resulting force that must beexerted to transport the casing downhole. However, expansion of thecuffs 29 provides substantial centralizing force so as to maintain thewell pipe 3 centralized within the wellbore 13 to thereby maximize theuniformity of the annular space 17 between the casing and well sidewall15. Also advantageously, the stored mechanical energy within each of thecuffs is combined by the collar to provide a substantial increase incentralizing force compared to a construction wherein the cuffs expandor retract independently. Finally, by aligning each cuff loop axisparallel to the pipe's longitudinal axis, one minimizes the obstructionto the flow of cement as it is pumped downhole.

According to certain embodiments, the invention includes an apparatusfor actuating a centralizer to centralize or center a pipe downhole. Thepipe has a longitudinal axis and a cylindrical exterior wall. Thecentralizer includes a plurality of circumferentially-spacedcentralizing members configured to be mounted to the cylindricalexterior wall of the pipe. The apparatus includes a lock configured tobe coupled to the centralizing members. The lock has been configured totransition from a locked position locking each of the centralizingmembers in a radially retracted position, and an unlocked positionallowing each of the centralizing members to transition from theradially retracted position to a radially expanded position. Theapparatus also includes an actuator coupled to the lock. The actuatorhas been configured to selectively transition the lock from the lockedposition to the unlocked position.

In further embodiments, the actuator may be configured to transition thelock from the locked position to the unlocked position in response to anincrease in pressure within the pipe. And in other embodiments, thecentralizer further includes a collar coupled to the centralizermembers. The collar may be configured to move relative to the exteriorwall of the pipe to transition the centralizing members from theradially retracted positions to the radially expanded positions. Thelock may include a pin configured to releasably engage a notch in thecollar and the pin may be seated in the notch for the lock in the lockedposition and the pin may be withdrawn from the notch with the lock forthe unlocked position.

The actuator may include a ring configured to rotate relative to the pinwhen the pin has been seated within the notch, according to certainembodiments. And additionally, the pin may be biased out of the notch.On other embodiments, the actuator further may include a ring disposedabout the pipe. The ring may include a recess and an indent. Theactuator may further include a strap with a first end and a second endcoupled to a toothed assembly having a plurality of teeth. The at leastone of the teeth may be configured to engage with the indent to rotatethe ring to align the recess with the pin. The actuator may beconfigured to transition the lock from the locked position to theunlocked position in response to an increase in tension in the strap,engagement between the one of the teeth and the indent, and rotation ofthe ring relative to the pin. The teeth may be configured to pivotrelative to the ring and slide along the ring in response to aretraction of the exterior wall of the pipe.

In certain embodiments, the centralizer further includes a collarcoupled to the centralizer members and the collar has been configured tomove relative to the exterior wall of the pipe to transition thecentralizing members from the radially retracted positions to theradially expanded positions. The lock may include solder coupled to thecollar and configured to prevent movement of the collar relative to thepipe. The actuator may be configured to at least partially melt thesolder. The pin may be releasably secured to the collar within the notchby solder and may include a central heating element configured toselectively melt the solder to allow the pin to withdraw from the notch.

In certain embodiments, the invention includes a centralizer forcentralizing a pipe downhole. The pipe has a longitudinal axis and acylindrical exterior wall. The centralizer includes a plurality ofcircumferentially-spaced centralizing members configured to be mountedto the cylindrical exterior wall of the pipe. Each centralizer memberhas a radially retracted position and a radially expanded position. Thecentralizer also includes a lock coupled to the centralizing members andthe lock has been configured to transition from a locked positionlocking each of the centralizing members in the radially retractedposition and an unlocked position allowing each of the centralizingmembers to transition from the radially retracted position to theradially expanded position. The centralizer also includes an actuatorcoupled to the lock. The actuator has been configured to selectivelytransition the lock from the locked position to the unlocked position.The actuator may be configured to transition the lock from the lockedposition to the unlocked position in response to an increase in pressurewithin the pipe.

Each centralizing member has a first end and a second end opposite thefirst end, so the first ends are extended away from the second ends inthe radially retracted positions and the first ends are contractedtoward the second ends in the radially expanded positions, according tosome embodiments. The first ends of the centralizing members may beconfigured to be affixed to the exterior surface of the pipe and asecond ends of the centralizing members may be configured to moverelative to the first ends and the exterior surface of the pipe. Thecentralizer may further include a collar coupled to the second ends ofthe centralizer members and a clamp band coupled to the first ends ofthe centralizer members. The collar may be configured to move relativeto the clamp band to transition the centralizing members from theradially retracted positions to the radially expanded positions.

The lock may include a pin configured to releasably engage a notch inthe collar so that when the pin has been seated in the notch with thelock in the locked position and the pin has been withdrawn from thenotch with the lock in the unlocked position resulting in the pin hasbeen biased out of the notch. The actuator may further include a ringdisposed about the pipe and the ring includes a recess and an indent.The actuator may further include a strap including a first end and asecond end coupled to a toothed assembly having a plurality of teeth sothat at least one of the teeth may be configured to engage with theindent to rotate the ring relative to the clamp band and to align therecess with the pin. The actuator may be configured to transition thelock from the locked position to the unlocked position in response to anincrease in tension in the strap, engagement between the one of theteeth and the indent, and rotation of the ring relative to the clampband. The teeth may be configured to pivot relative to the ring andslide along the ring in response to a retraction of the exterior wall ofthe pipe. The pin may be releasably secured to the collar within thenotch by solder and the pin may include a central heating elementconfigured to selectively melt the solder to allow the pin to withdrawfrom the notch.

According to certain embodiments, the invention includes a string ofcasing pipe with a centralizer of an embodiment coupled to it. In otherembodiments, the invention includes a method for centralizing a pipedownhole. The pipe has a cylindrical exterior wall and a longitudinalaxis. The method includes the steps of locking, inserting, andactuating. The first step includes locking a plurality of centralizingmembers in a radially withdrawn position proximal the exterior wall ofthe pipe. The second step includes inserting the centralizing membersdownhole after the step of locking. The third step includes actuatingthe centralizing members after the step of inserting from the radiallywithdrawn position to a radially expanded position with the centralizingmembers distal the exterior wall of the pipe. The locking step furthermay include inserting a pin within a notch in a collar moveably disposedabout the exterior wall of the pipe so each centralizer member has anend coupled to the collar. The actuating step further includes 1)increasing the pressure within the pipe, 2) expanding the exterior wallof the pipe in response to the increase in pressure within the pipe, 3)engaging one of a plurality of teeth with an indent on a ring disposedabout the pipe during the step of expanding, the ring including arecess, 4) rotating the ring about the pipe as a result of theengagement in the step of engaging, 5) aligning the recess with the pinduring the step of rotating, and 6) receiving the pin into the recessand withdrawing the pin from the notch in the collar. The locking stepfurther may include securing the pin within the notch with solder so thestep of actuating further includes activating a central heating elementdisposed within the pin to melt the solder and melting the solder withthe central heating element.

According to one embodiment, an apparatus for actuating a centralizer tocentralize a pipe downhole includes a lock, a pin, and an actuator. Thepipe has a longitudinal axis and a cylindrical exterior wall. Thecentralizer has plurality of circumferentially-spaced centralizingmembers and the centralizer configured to be mounted to the cylindricalexterior wall of the pipe. The lock may be configured to be coupled tothe centralizing members and the lock may be configured to transitionfrom a locked position locking each of the centralizing members in aradially retracted position and an unlocked position allowing each ofthe centralizing members to transition from the radially retractedposition to a radially expanded position. The lock includes a pinconfigured to be seated within a notch formed in a collar coupled to thecentralizing members. The collar has been configured to move relative tothe exterior wall of the pipe to transition the centralizing membersfrom the radially retracted positions to the radially expandedpositions. The pin has been biased out of the notch and the pin has beenseated within the notch when the lock is in the locked position and hasbeen withdrawn from the notch when the lock is in the unlocked position.The actuator coupled to the lock has been configured to selectivelytransition the lock from the locked position to the unlocked position.The actuator includes a ring disposed about the pipe and the ringincludes a recess and an indent. The actuator also includes a strapincluding a first end and a second end coupled to a toothed assemblywith a plurality of teeth so at least one of the teeth has beenconfigured to engage with the indent to rotate the ring to align therecess with the pin in response to an expansion of the exterior wall ofthe pipe. The teeth have been configured to pivot relative to the ringand slide along the ring in response to a retraction of the exteriorwall of the pipe.

While preferred embodiments have been shown and described, modificationsthereof can be made by one skilled in the art without departing from thescope or teachings herein. The embodiments described herein areexemplary only and are not limiting. Many variations and modificationsof the systems, apparatus, and processes described herein are possibleand are within the scope of the disclosure. For example, the relativedimensions of various parts, the materials from which the various partsare made, and other parameters can be varied. Accordingly, the scope ofprotection is not limited to the embodiments described herein, but isonly limited by the claims that follow, the scope of which shall includeall equivalents of the subject matter of the claims. Unless expresslystated otherwise, the steps in a method claim may be performed in anyorder. The recitation of identifiers such as (a), (b), (c) or (1), (2),(3) before steps in a method claim are not intended to and do notspecify a particular order to the steps, but rather are used to simplifysubsequent reference to such steps.

What is claimed is:
 1. An apparatus for actuating a centralizer tocentralize a pipe downhole, the pipe having a longitudinal axis and acylindrical exterior wall, the centralizer including a plurality ofcircumferentially-spaced centralizing members mounted to the cylindricalexterior wall of the pipe, the apparatus comprising: a lock coupled tothe centralizing members, wherein the lock transitions from a lockedposition locking each of the centralizing members in a radiallyretracted position to an unlocked position allowing each of thecentralizing members to transition from the radially retracted positionto a radially expanded position; and an actuator coupled to the lock,wherein the actuator selectively transitions the lock from the lockedposition to the unlocked position in response to an increase in pressurewithin the pipe.
 2. The apparatus of claim 1, wherein the centralizerfurther comprises a collar coupled to the centralizer members, whereinthe collar moves relative to the exterior wall of the pipe to transitionthe centralizing members from the radially retracted positions to theradially expanded positions; wherein the lock includes a pin releasablyengages a notch in the collar; wherein when the pin seated in the notchwith the lock in the locked position and the pin withdrawn from thenotch with the lock in the unlocked position.
 3. The apparatus of claim2, wherein the actuator comprises a ring which rotates relative to thepin when the pin seated within the notch.
 4. The apparatus of claim 3,wherein the pin biased out of the notch.
 5. The apparatus of claim 4,wherein the pin is releasably secured to the collar within the notch bysolder; and wherein the pin includes a central heating elementselectively melts the solder to allow the pin to withdraw from thenotch.
 6. The apparatus of claim 2, wherein the actuator furthercomprises: a ring disposed about the pipe, wherein the ring includes arecess and an indent; a strap including a first end and a second endcoupled to a toothed assembly comprising a plurality of teeth; whereinat least one of the teeth engages with the indent to rotate the ring toalign the recess with the pin.
 7. The apparatus of claim 6, wherein theactuator transitions the lock from the locked position to the unlockedposition in response to an increase in tension in the strap, engagementbetween the one of the teeth and the indent, and rotation of the ringrelative to the pin.
 8. The apparatus of claim 7, wherein the teethpivot relative to the ring and slide along the ring in response to aretraction of the exterior wall of the pipe.
 9. The apparatus of claim1, wherein the centralizer further comprises a collar coupled to thecentralizer members, wherein the collar moves relative to the exteriorwall of the pipe to transition the centralizing members from theradially retracted positions to the radially expanded positions; andwherein the lock comprises solder coupled to the collar and preventmovement of the collar relative to the pipe; wherein the actuator atleast partially melts the solder.
 10. A centralizer for centralizing apipe down hole, the pipe having a longitudinal axis and a cylindricalexterior wall, the centralizer comprising: a plurality ofcircumferentially-spaced centralizing members mounted to the cylindricalexterior wall of the pipe, wherein each centralizer member has aradially retracted position and a radially expanded position; a lockcoupled to the centralizing members, wherein the lock transitions from alocked position locking each of the centralizing members in the radiallyretracted position to an unlocked position allowing each of thecentralizing members to transition from the radially retracted positionto the radially expanded position; an actuator coupled to the lock,wherein the actuator selectively transitions the lock from the lockedposition to the unlocked position in response to an increase in pressurewithin the pipe.
 11. The centralizer of claim 10, wherein eachcentralizing member has a first end and a second end opposite the firstend, wherein the first ends are extended away from the second ends inthe radially retracted positions and the first ends are contractedtoward the second ends in the radially expanded positions; wherein thefirst ends of the centralizing members are affixed to the exteriorsurface of the pipe and the second ends of the centralizing members moverelative to the first ends and the exterior surface of the pipe; andwherein the centralizer further comprises a collar coupled to the secondends of the centralizer members and a clamp band coupled to the firstends of the centralizer members, wherein the collar moves relative tothe clamp band to transition the centralizing members from the radiallyretracted positions to the radially expanded positions.
 12. Thecentralizer of claim 11, wherein the lock includes a pin whichreleasably engages a notch in the collar; wherein when the pin seated inthe notch with the lock in the locked position and the pin withdrawnfrom the notch with the lock in the unlocked position; wherein the pinbiased out of the notch.
 13. The centralizer of claim 12, wherein thepin releasably secured to the collar within the notch by solder; andwherein the pin includes a central heating element which selectivelymelts the solder to allow the pin to withdraw from the notch.
 14. Thecentralizer of claim 11, wherein the actuator further comprises: a ringdisposed about the pipe, wherein the ring includes a recess and anindent; a strap including a first end and a second end coupled to atoothed assembly comprising a plurality of teeth; wherein at least oneof the teeth engages with the indent to rotate the ring relative to theclamp band and to align the recess with the pin.
 15. The centralizer ofclaim 14, wherein the actuator transitions the lock from the lockedposition to the unlocked position in response to an increase in tensionin the strap, engagement between the one of the teeth and the indent,and rotation of the ring relative to the clamp band; and wherein theteeth pivot relative to the ring and slide along the ring in response toa retraction of the exterior wall of the pipe.
 16. A string of casingpipe including a centralizer of claim 10 coupled thereto.
 17. A methodfor centralizing a pipe downhole, the pipe having a cylindrical exteriorwall and a longitudinal axis, the method comprising: locking a pluralityof centralizing members in a radially withdrawn position proximal theexterior wall of the pipe by inserting a pin within a notch in a collarmoveably disposed about the exterior wall of the pipe, wherein eachcentralizer member has an end coupled to the collar; inserting thecentralizing members downhole after the step of locking; and actuatingthe centralizing members after the step of inserting from the radiallywithdrawn position to a radially expanded position with the centralizingmembers distal the exterior wall of the pipe, wherein the step ofactuating comprises: increasing the pressure within the pipe; expandingthe exterior wall of the pipe in response to the increase in pressurewithin the pipe; engaging one of a plurality of teeth with an indent ona ring disposed about the pipe during the step of expanding, the ringincluding a recess; rotating the ring about the pipe as a result of theengagement in the step of engaging; aligning the recess with the pinduring the step of rotating; and receiving the pin into the recess andwithdrawing the pin from the notch in the collar.
 18. A method forcentralizing a pipe downhole, the pipe having a cylindrical exteriorwall and a longitudinal axis, the method comprising: locking a pluralityof centralizing members in a radially withdrawn position proximal theexterior wall of the pipe by inserting a pin within a notch in a collarmoveably disposed about the exterior wall of the pipe, wherein eachcentralizer member has an end coupled to the collar, and securing thepin within the notch with solder; inserting the centralizing membersdownhole after the step of locking; and actuating the centralizingmembers after the step of inserting from the radially withdrawn positionto a radially expanded position with the centralizing members distal theexterior wall of the pipe, wherein the step of actuating furthercomprises: activating a central heating element disposed within the pinto melt the solder; and melting the solder with the central heatingelement.
 19. An apparatus for actuating a centralizer to centralize apipe downhole, the pipe having a longitudinal axis and a cylindricalexterior wall, the centralizer including a plurality ofcircumferentially-spaced centralizing members mounted to the cylindricalexterior wall of the pipe, the apparatus comprising: a lock coupled tothe centralizing members; wherein the lock transitions from a lockedposition locking each of the centralizing members in a radiallyretracted position and an unlocked position allowing each of thecentralizing members to transition from the radially retracted positionto a radially expanded position; wherein the lock includes: a pin seatedwithin a notch formed in a collar coupled to the centralizing members;wherein the collar moves relative to the exterior wall of the pipe totransiton the centralizing members from the radially retracted positionsto the radially expanded positions; wherein the pin biased out of thenotch; wherein the pin seated within the notch when the lock in thelocked position and withdrawn from the notch when the lock in theunlocked position; an actuator coupled to the lock, wherein the actuatorselectively transitions the lock from the locked position to theunlocked position wherein the actuator includes: a ring disposed aboutthe pipe, wherein the ring includes a recess and an indent; a strapincluding a first end and a second end coupled to a toothed assemblycomprising a plurality of teeth; wherein at least one of the teethengages with the indent to rotate the ring to align the recess with thepin in response to an expansion of the exterior wall of the pipe; andwherein the teeth pivot relative to the ring and slide along the ring inresponse to a retraction of the exterior wall of the pipe.